AC light turns itself off, blows hot

Discussion in 'Prime Care, Maintenance and Troubleshooting' started by Shameless, Jul 5, 2025 at 12:12 PM.

  1. Shameless

    Shameless Member

    Joined:
    Mar 7, 2014
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    Location:
    Western Massachusetts
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    Got a 2017 Prime. Started blowing warmer. Now it's basically got no cooling power at all. I figured maybe I just needed a refrigerant top-up. That led me down a rabbit hole of trying to figure out which refrigerant, and whether I should do it myself, as I have in every other car I've had. Still haven't figured out the answer to either of those. I have a can of R134a.

    Anyway. Connected the cheapo gauge with the can, and even though I lost a little refrigerant in the process of just checking, I think, the refrigerant was still in the green. (Can't remember for sure right now, but probably 35 or so?)

    Stopped there to do more research. Checked error codes with the button-pushing trick, and got 00. Which means no errors, correct?

    But here's where I'm really puzzled: I had the AC and recirc buttons on, just to see if anything would happen. In a few minutes, both the lights were off. Repeated to make sure I wasn't missing something, and yep, for sure. It's done it repeatedly.

    When I hit AC, I hear a pretty loud sound which I assume is the compressor.

    I just paid a boat load to get my daughter's AC fixed (on a Honda), so if this is doable without trying to find a Prius AC specialist, that sure would be nice.

    Any ideas? Thanks!
     
  2. Zannajade

    Zannajade New Member

    Joined:
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    Location:
    hongkong
    Vehicle:
    2017 Prius PHV
    Model:
    N/A
    May be you could try using this method to fix it.
    1. Unplug the high-voltage plug and low-voltage plug of the air conditioning compressor.

    2. Check the insulation of the high-voltage system:

    1) Adjust the insulation meter to the 500V/1000V range. It depends on the vehicle's high-voltage system. If the vehicle has a system below 500V, use the 500V range; if it is a 500-1000V system, use the 1000V range.

    2) Connect the positive pole of the insulation meter to one end of the compressor's high-voltage connector, and the negative pole to the housing. As shown in the figure, the measured value should be >550MΩ. The specified insulation value varies with different vehicle models, generally 500Ω/V. For example, if the vehicle has a 400V system, the minimum should be 20MΩ, but the specific value should refer to the definition of the vehicle manufacturer. If the insulation value is lower than this value, it indicates a compressor failure, and it is recommended to replace the compressor.

    **Note**: The low-voltage system does not need to be tested for insulation. The instantaneous output voltage of the insulation meter is very high, which will damage the low-voltage system circuit.

    3. Check whether the positive and negative poles of the high-voltage connector are short-circuited, as shown in the figure. A short circuit indicates damage to the compressor circuit, and it is recommended to replace the compressor; no short circuit indicates normal, and then proceed to the next step.

    4. Check the IGBT and motor of the air conditioning compressor control board.

    It is determined by measuring the voltage drop between the positive and negative poles of the high-voltage connector. Adjust the multimeter to the diode range. The positive pole of the multimeter touches the negative high-voltage terminal, and the negative pole touches the positive high-voltage terminal. If there is a normal voltage drop, it can be confirmed that the compressor IGBT and motor are basically normal, as shown in the left figure.

    5. The scroll disc of the air conditioning compressor is prone to damage, and the characteristic of damage is abnormal noise.

    The main reasons for the damage of the air conditioning compressor scroll include excessive moisture, excessive impurities, oil shortage or insufficient lubrication, motor damage, liquid hammer, high-temperature burnout, etc.

    6. Compressor stator damage.
    The main reasons for stator damage include burned motor coils, poor condenser heat dissipation, exhaust valve leakage, stator winding insulation layer damage (short circuit) and open circuit.

    The following figure shows the rotor and rotor coil:

    **Note**: Before disassembling and inspecting the air conditioning compressor, the refrigerant inside should be recovered. After the inspection is completed and installed, the refrigerant inside should be refilled. Due to different vehicle models, the filling amount refers to the maintenance manual of the corresponding vehicle model.